Pressure cooker test

Let a drop of water drop on the pressure cooker while sterilizing.
If the drop boils like underneath, the temperature is around 250°F(121°C) and the pressure cooker is working properly.

Why does this happen?

A pressure cooker operating under pressure is very hot, it is quite much hotter than the boiling point of water at 1 atmosphere (212°F=100°C). If the pressure cooker is of the "standard" kind, it will be at 250°F = 121°C .

If you put a small amount of water, a drop, on the surface of the lid of the pressure cooker while the pressure cooker is hot and under pressure, the drop of water will begin to boil vigorously and will evaporate in 2-3 seconds, since the surface of the pressure cooker is so much hotter than the boiling point of water at the atmospheric pressure.

If the pressure cooker doesn't work properly, i.e. if the pressure doesn't build up as it should, the pressure cooker temperature will be the same or only slightly above as the boiling point of water at atmospheric pressure. If you were to drop a drop of water on such a cooker, the drop would only sit there and slowly evaporate over the course of a longer time span.